Application of density functional theory for organic, inorganic, and biochemical molecules
Richardson, Nancy Arline
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I have applied density functional theory (DFT) to questions in organic, inorganic, organometallic, and biochemical systems. In this dissertation I attempt to lay groundwork for improvement of DFT. While accessible with more computationally demanding methods, DFT is a reasonable choice for some small molecule studies, especially when these results coincide with those of the methods demanding more computational resources. In other cases DFT is the only accessible method. Work investigating trends in verticle groups employed both computationally demanding methods and DFT. Group 14 congeners of formic and acetic acid as well as three other isomers (dihydroxy carbene, hydroperoxycarbene, and dioxirane) showed an energetic preference for divalency of Si to Pb with the dihydroxy carbenes being the most stable isomer for each congener; however, comparison of only the hydroperoxycarbene and formic acid showed greater stability for the acid isomer for all congeners through plumbanonic acid. In these cases, results for DFT were similar to results of highly demanding computational methods. Computationally accessible only with DFT were the organometallic and biochemical molecules studied in this dissertation. The question of the structure, thermodynamics, and mystery of the nonexistence of Cr2 (CO)11 was explored. The lowest energy stucture (of Cs) symmetry was determined to be thermodynamically unstable. The other vein of DFT application was the e ect of excess negative charge in nucleic acid base (NAB) pairs. Isolated NAB pairs bind charge with an appreciable electron a nity. This excess charge signi cantly perturbs the geometry of the pair, especially of the pyrimidine ring. These applications show the exibility of DFT as well as its limitations: trends and brackets in energetics, as well as geometric conformations are determinable while isolated exact results are not.